Sorry to hear you're having trouble cancelling. Have you tried these steps: Settings > Membership > Click Pause or cancel membership > Cancel membership? More info: https://yt.be/help/b1LG . Let us know.
Since we don't have access to cancel the subscription for you, we'd recommend contacting our live support team using chat, phone or email for further help with this: https://yt.be/help/EQng . Hope this gets resolved.